The present invention relates to a tripod, typically used for supporting an optical instrument such as a camera. More particularly, the invention provides a tripod which conforms to the requirements of mobile users needing fast and secure set-up and after use, fast folding into a compact, low-weight package.
Tripods are used to provide a temporarily-fixed support for surveying instruments; still and TV and cinematography cameras; lighting fixtures, reflectors, security equipment and medical and laboratory equipment. Cameras such as are used by television crews can be of considerable weight, yet need to be supported steadily to provide best results. A tripod, provided with individually adjustable legs offers such support even when set up on an uneven or stepped surface. News reporters, for newspapers, magazines or TV are typical users of a tripod, but their needs are not well served by prior art devices. Many leg adjustment mechanisms rely on turning lock screws during set-up and releasing same after filming. Failure to securely lock one of the legs causes tripod collapse and likely damage to a costly camera, yet the task is particularly difficult in cold weather. Applying too much torque to a lock-screw can damage the screw thread or the leg member with which the screw is in contact. Most locking devices prevent movement in both axial directions, and so inhibit extension of a leg without prior lock release. As three legs require locking/unlocking, such devices require too much time to set-up and dismantle, and for news camera personnel the person or event to be photographed may be unavailable by the time the camera is properly supported for operation.
The tripod is by its nature a mobile item which is carried by its users, wherefore light weight is a self-evident requirement. Yet some commercially-available tripods, using aluminium tubes as leg members, weigh between 5 and 10 kg.
In U.S. Pat. No. 5,320,316 Baker discloses a tripod, the claimed innovation concerning primarily the leg structure. The proposed locking device is a ring floatingly supported in a groove. The inner edges of the ring lock against the outer surface of the leg tube. The present inventor considers this form of lock to be usable only against a metal leg tube, as it would damage a plastic tube. Consequently a tripod made accordingly will have an undesirably high weight.
Johnson et al in U.S. Pat. No. 5,503,357 specify threaded holes and screws for locking a tripod. When locked, the legs can not be extended outwards. One of the disadvantages of lock-screws is that unless tightened with considerable force, inadvertent leg retraction can occur under a heavy load. Commercial catalogue LNORD 99, G issued by Lino Manfrotto and Co. (Italy) lists a wide range of tripods. The manufacturer uses aluminium tubes for construction of legs for the more heavy duty tripods. This results in high weight. Tripods intended to support 20 kg weigh between 3.6 to 7.9 kg. The only model (132X) able to support 30 kg weighs 6.9 kg. Telescopic joints are individually locked by threaded lock screws.
OCONNOR (Costa Mesa, USA) has issued a 1999 commercial catalogue featuring a range of tripods having carbon fiber legs. Maximum allowed load is between 27 and 91 kg, depending on the model, and corresponding weights of the tripod are between 4.2 and 10.8 kg. A lever-operated ring under the top casting releases all 3 legs simultaneously. The legs are individually adjustable by means of lock levers. However the user is required to push down the leg lock levers to lock the joints, as locking is not automatic.
The Sachtler company (www.sachtler.de/seiten/whats-up/new-speedlock.htm) has recently disclosed a tripod (model HD) having carbon fiber legs and provided with a locking device which controls an upper and a lower telescopic joint simultaneously. Users must release all three clamps to extend legs. Threaded lock screws are used on the spreader arms. The tripod weight of 3 kg is stated, but no maximum extended height is given.
It is therefore one of the objects of the present invention to obviate the disadvantages of prior art tripods and their associated locking devices and to provide a tripod which can be deployed and folded without the user having to operate any locking device.
It is a further object of the present invention to provide a locking device which is faster to operate than a lock screw.
A further object is to provide a tripod which has a low self-weight relative to its extended height and the weight of the supported load.
Yet a further object of the present invention is to provide a tripod wherein the force of leg locking automatically adjusts itself in accordance with the load being supported, and totally eliminates the risk of inadvertent omission to lock any or all legs.
The present invention achieves the above objects by providing a fast-deployable light-weight tripod, comprising:
a) a center support for supporting a load, provided with three peripheral hinge members;
b) three multi-stage telescoping leg assemblies each attached to one of said hinge members, each leg assembly comprising at least two compression-resistant members interconnected by a telescopic joint;
c) at least one cam locking unit associated with each telescopic joint, each locking unit having a first engaged position preventing relative axial movement which would shorten the length of said leg assembly, and a second disengaged position wherein said assemblies are free to move in either axial direction, each locking unit being urged towards its engaged position for automatic locking of said tripod in its deployed position with said cam locking being effected by pressure on said cam unit from its associated extended leg; and further comprising:
d) a hand accessible release element for each leg assembly for independently releasing said at least one cam locking unit associated therewith, thereby enabling the shortening of the length of said assembly.
In preferred embodiments of the present invention, said tripod further comprises a foldable hinged three-arm restriction member hingedly attached to said legs to prevent excessive spread of said leg assemblies.
In a preferred embodiment of the present invention there is provided a tripod wherein actuation of a hand-accessible element disengaging a cam locking unit associated with a lower telescopic joint is connected to a linkage arranged to simultaneously disengage at least one cam locking unit controlling an upper telescopic joint.
In especially preferred embodiments of the present invention, said tripod comprises three compression resistant members interconnected by an upper and a lower telescopic joint and further comprises at least one cam locking unit associated with each telescopic joint, each locking unit having a first engaged position preventing relative axial movement which would shorten the length of said leg assembly, and a second disengaged position wherein said assemblies are free to move in either axial direction, and wherein said cam locking unit allows extension of its associated leg assembly while in its engaged position and wherein said hand-accessible release element arranged to disengage said lower telescopic joint is connected to a linkage arranged to simultaneously disengage at least one cam locking unit controlling said upper telescopic joint.
In a most preferred embodiment of the present invention there is provided a tripod wherein the hinged three-arm restriction member, is when folded, positioned to press against all three release levers, thus disengaging cam locking units on all legs at both telescopic joints, whereby the tripod can be folded and retracted very quickly without the need for separate manual release of any of the locking devices, although it is possible in smaller embodiments of the present invention, which do not include the restriction member, to arrange the release levers so that when the three legs are brought together, the release levers interact with each other, disengaging the cam locking units on all the legs to enable the rapid retraction and telescoping compactation thereof.
Yet further embodiments of the invention will be described hereinafter.
It will thus be realized that the novel light-weight tripod of the present invention meets the requirements of fast set up, allows individual leg extension, safely supports any load within its range and yet avoids possible damage due to excessively hard manual locking. In particular, folding of the tripod is faster than any prior-art device as no locking device whatsoever need be operated manually for this purpose.